That would amount to a nine-month stoppage overall. The world’s widest tunnel-boring machine halted Dec. 7 when it overheated, and sand was found in the grease around the main bearing. Bertha has advanced only four feet since then.

Dixon said Friday that all seven rubberized seals that protect the bearing must be replaced, and fixes might be needed to the bearing or to other parts in the machine. Repairs will require digging a deep pit to remove or bypass the giant cutterhead and other connected parts.

Representatives of the bearing manufacturer, Rothe Erde of Germany, have inspected the machine’s front end. Asked in an interview if sand or salt water made it all the way into the rolling parts inside the bearing, Dixon said: “There’s a suspicion they might have, but they don’t know that now.”

That’s a change from earlier conjecture by both Dixon and officials of the state Department of Transportation (DOT), who had expressed confidence the bearings were OK. A replacement bearing is stored at Osaka, Japan, home of machine builder Hitachi-Zosen, Dixon said.

He called his own Sept. 1 date slightly optimistic. “What we try to do in construction is set a goal and get everybody focused on that,” he said.

An expert review panel report this week said the tunnel will slide a few months past the Dec. 31, 2015, completion date to open for traffic, and instead likely be done by mid-2016. Dixon said STP hasn’t done its own schedule review yet.

A full rescue plan isn’t due from Hitachi for another 10 days or so, he said, but the team has narrowed its options to three — all of which entail building a pit that’s 120 feet deep in front of the machine, near South Main Street. Bertha would then drive forward and break through a concrete wall to enter the work zone.

Meanwhile, the viaduct will be closed from 6 a.m. to 6 p.m. both Saturday and Sunday, for routine maintenance and repairs, the DOT says.

About The Today File

The Today File is a general news blog featuring real-time coverage of Seattle and the Northwest. It is reported by the news staff of The Seattle Times and includes stories from The Associated Press and McClatchy-Tribune Information Services.